Phosphate coating of metals



Patented May 8, 1945 PHOSPHATE s PATE 2,375,468 COATING METALS Ni ori ce 'Wilfred James Cliflord and Henry Heward Adams, Brentford, England, assignors to Parker Rust-Proot Company, Detroit, Mich., a corporation of Michigan J No Drawing. Application December 13, 1941, Serial No. 422,872. In Great Britain-February 9 Claims. (oi. 148-6) This invention relates to the treatment of metals, especially iron or steel, for instance to the treatment of metals with phosphate coating solutions in order to improve the resistance of the metals to corrosion or to provide a corrosion resisting base for paints. This application is a continuation in part of application, Serial No. 254,238, filed February 2, 1939, issued as Patent No. 2,295,545, September 15, 1942. This application covers the disclosed coating chemicals as a composition of matter, the coating of zinciferous surfaces not disclosed in said prior application, and the use of 'nitro-guanidine which is alternat'ive to the three species specifically claimed in said prio'r application.

It is an object of the invention to accelerate the action of reagents which attack a metal Sill;- face. a

It is a-further object or the, invention to 86- celeratethe action of phosphate coating solutions, such as zinc, manganese and the like, i. e., to reduce the time taken by'the coating solution to form a complete coating, or to reduce 'the temperature, or to obtain a better coating .in a given time under given conditions than if the compound were not present.

Where phosphate and similar. coatings are being employed, they may be applied to the metal in any suitable manner, for instance by" spraying, brushing, fiowing immersion or methods.

ditions used, of various compounds which may be employed according to the inventionare given in the following table, the results being arrived at by adding the compound to a solution of zinc dihydrogen' phosphate having a normality of N/ free acid (determined by titrating with the with other accelerators and with other acid phosphate coating solutions, for instance metal- It has now been found that the action of reagents which attack metal' surfaces, and especially phosphate coating solutions, are improved by incorporating therein a nitro group.

- As illustrative of the compounds which may be employed to provide the nitro group we have nitromethane, nitrobenzene, 0-, m.- and p-nitrophenols, nitrobenzoic acids, picric acid, nitrourea,

nitroguanidine, nitrourethane, o-, m-, and p-nitraniline, oand p-nitrobenzoic acid and m-dinitrobenzene. a

The optimum concentration of the; compound to provide the accelerating group in'the reagent attacking the metal surface differs with different compounds but in the case of phosphate coating solutions is in general from about .01-% to .4% by weight of the solution. The proper amount of accelerator forbest results may be easily determined in any case bystarting the solution off with a small amount of the accelerator and increasing the amount added to the phosphate coating solution until the desired acceleration is obtained.

aid of methyl orange indicator) and N/5 total acid (determined-by titratingwith the aid of phenolphthalein indicator) and treating a cleaned, steel sheet for two minutes at 80 C. The cleaned steel sheet referred to here and in the examples given below is a steel sheet in its original bright rolled condition rendered substantially free from grease by wiping with clean white spirit.

Optimum submmw concentration Percent Picric acid. 0. Nitroguanidine 0. Nitrobenzene.-. 0. Nitrometlmne. 0. N itrourethenei 0. mor p-Nitrophenol. 0. Nitrourea 0. m-Nitrobenzolc acid 0 o-Niti'ophenol 0.

While the compounds of the invention may be the only accelerators present in the coat ng bath, they may also be, employed in conJunction llc accelerators such as copper compounds, or

oxidizing agents such as nitrates or nitrites.

The presence of copper ions appears to promote heavier and darker coatings and the presence of a nitrate, such as zinc nitrate, appears to give a slight further acceleration.

Certain of the accelerating compounds of the invention are so effective that coatings can be producedi'rom phosphate solutions containing them in the cold as is the case with nitroguanidine. I1 5 The invention is illustrated by the following examples:

Example 1 This is an example of the use of nitroguanidine to provide the nitro group to accelerate a coating operation to sogreat an e ttent that'it can be effected in the cold.

e A cold solution of manganese phosphate having a normality of about N/100 free acid (determined by titrating with the aid of methyl orange The optimum concentrations, under theconindicator) and N/51 total acid (determined by,

in a hot solution.

titrating with the aid' or phenolphthalein indicator) will not produce a coating on a cleaned I A zinc dihydrogen phosphate solution with norinality'i of about N/ 20 free acid determined by titrating with the aid of methyl orange indicator) i and N/B total acid (determined by titr ating' with the aid of phenolphthalein indicator), to which i 0.2% of nitroguanidine has been added, will at 80" C. produce an adherent coating on a cleaned steel sheet in two minutes. In the absence of the nitroguanidine only a soft non-adherent coating I is produced in '10 minutes.

Example 3 with-a phosphate coating by treating it ata temperature from to 80C, with a'solution of zinc or manganese dihydrogen phosphate, of concentration N/5 when determined using phenol-v phthalein as indicator, containing 0.05% or" nitroguanidine.

- ous surfaces with an acid phosphate coating solu- I Ax cleanecl steel sheet can be successfully coated If in any of the above examples 0.001% of. I

copper (calculated as the metal) is added. to the solution,'for'instance in the form of the nitrate.

.or carbonate, a darker and'slightly heavier coating is'obtained, and the addition of zinc nitrate results in a slight further acceleration".

i a While the invention has been illustrated by the treatment of steel, it is also useful in the coating of other metallic surfaces, such as surfacescontaini ig zinc and alloys thereof. V What we claim is:

A composition consisting essentially of acid phosphate coating chemicals and an organic compound which 'contains the nitro group in sufficient quantity to act as an accelerator;

' .2. A composition in accordance with claimfl I drog en phosphate, 7 3. A composition in accordance with claim 1 and in. which the acid phosphate is zinc dihy-' dihydrogen phosphate.

4. The process which comprises treating zinciferous surfaces with an acid phosphate coating solution containing an organic compound which and in which the'acid phosphate is manganese itself contains the'nitro group in sufficient quantity to act as an accelerator-until there is obtained upon the metallic surface a phosphate coating bonded to the metallic surface by chemical reaction therewith. 7

5. A process which comprises treating zinciferone surfaces with an acid phosphate coating soluc tion containing zinc and an organic compound having the nitr'o group in sufficient" quantity to act as an accelerator, until there is obtained upon the metallicgsurface a phosphate coating bonded:

thereto by chemicalreaction. g

6. A process which comprises treating zincifertion containing manganese and an organic compoundhaving the nitro-grOup in sufiicient quantityto acts as an accelerator until there is obtained upon the metallic surface a' phosphate coating bonded thereto by chemical reaction.

- 7. A process whichcomprises treating a zinciferous surface with an acid phosphate coating solution containing a nitrobenzene in an amount. sufiicient to have an accelerating efiect upon the coating action until a visible protective phosphate coating is obtained'upon the-metallic surface.

8. A process'which comprises treating a zinciferous surface'with an acid phosphate coating solution containing a nitrophenol in an amount suilicient to have an accelerating effect upon the coating action until a visible protective phosphate coating is obtained upon the metallic surface.

"9. A process which. comprises treating a sur face of one of -the group consisting of ferrous andzinciferous surfaceswith an acid phosphate vcoating'solution containing nitroguanidine in an amount suflicient'to have an accelerating effect;

upon the coating action untila visible protective phosphatecoatingis obtained upon the metallic surface;

HENRY HEWARD ADAMS,

.IWILFRED JAMES CLIFFORD. 

